1. Field of the Invention
The present invention relates to a pen-shaped coordinate pointing device which indicates a position to be measured and an operation by an operator to a position detecting device, such as a tablet, for measuring the position.
2. Description of the Related Art
Conventionally, a pointing device, called a “pen and tablet”, is used as one of the input devices for computers. The pen and tablet is a combination of a platelike tablet and an input pen to be operated on the tablet by an operator. When the operator indicates an arbitrary position on the tablet with the input pen, the position is detected by the tablet and information about the position is output to a computer.
The present applicant has proposed various input pens and the like for pens and tablets, as disclosed in, for example, Japanese Examined Utility Model Application Publication No. 5-4034. An example of a conventional input pen will now be described with reference to FIG. 13.
FIG. 13 is a cross-sectional view showing the general structure of an input pen 90 as an example of a conventional input pen. Components of the input pen 90 are housed in a penholder 91 which has almost the same shape as that of a writing instrument, such as a ballpoint pen or a fountain pen.
At the leading end of the penholder 91, a lead 92 is disposed so as to be connected to the interior of the penholder 91. The base end of the lead 92 is inserted in a through hole formed in a ferrite core 94 and is fixed to a lead holder 96. The lead holder 96 is fixed to the penholder 91 with a spring 97 therebetween.
The lead 92 has a ferrite chip 93 therein. In a non-operation state of the input pen 90, approximately two-thirds of the ferrite chip 93 is placed in the through hole of the ferrite core 94. The lead 92 is supported by the spring 97 together with the lead holder 96 so that it can move in the direction of expansion and contraction of the spring 97, that is, in the axial direction of the penholder 91, and along the through hole of the ferrite core 94.
The ferrite core 94 is cylindrical and has a through hole extending in the longitudinal direction, in which the lead 92 is placed. A coil 95 is wound on the outer side face of the ferrite core 94 and is connected to a capacitor 98 in the penholder 91 so as to form a tuning circuit 99.
The tuning circuit 99 of the input pen 90 is excited in response to radio waves of a predetermined tuning frequency, for example, a frequency fo, output from a tablet (not shown), and induced voltage is induced in the coil 95. When the output of the waves is stopped, radio waves of a predetermined frequency are output from the coil 95 because of a current passing based on the induced voltage. By receiving the waves output from the tuning circuit 99 by the tablet, the position of the input pen 90 on the tablet can be detected.
The input pen 90 is operated so that the leading end of the penholder 91 is pressed against the tablet. During operation, the lead 92 is pushed in the penholder 91 and the ferrite chip 93 built in the lead 92 is moved toward the base end inside the ferrite core 94.
Since the coil 95 is wound on the ferrite core 94, as described, when the positional relationship among both ends of the ferrite core 94 and the ferrite chip 93 is changed, the inductance of the coil 95 is also changed. Therefore, in the tuning circuit 99 including the coil 95, the inductance of the coil 95 is changed by the movement of the ferrite chip 93, thereby changing the tuning frequency of the tuning circuit 99.
In this case, when a radio signal of a frequency fo is output from the tablet, the phase of the induced voltage produced in the coil 95 shifts from that in a non-operation state due to the change in tuning frequency of the tuning circuit 99. For this reason, the tuning circuit 99 outputs radio waves which are different in phase from the waves output from the tablet.
Accordingly, operation of the input pen 90 can be detected by exciting the tuning circuit 99 by outputting radio waves from the tablet and by detecting the phase difference between the waves and radio waves output from the tuning circuit 99.
As described in the above example, the conventional pen and tablet is easy to use because there is no need to connect the tablet and the input pen, and the operational feeling thereof is similar to that of typical writing instruments, such as fountain pens and ballpoint pens.
The conventional input pen, such as the above-described input pen 90, has a size similar to that of typical writing instruments, such as ballpoint pens, and is suited for use particularly in desktop computers and the like.
In recent years, size reduction of electronic devices has been achieved; for example, portable electronic devices, called “Personal Digital Assistants (PDA)” have become widespread. For this reason, there has also been a demand for size reduction of input devices for use in small electronic devices. It is, however, difficult to achieve a substantial size reduction without changing the structures of the conventional input pens.
As an example, the above-described input pen 90 must not only be shortened but must also be thinned for the purpose of size reduction. Therefore, the ferrite core 94 and the lead 92 must also be thinned.
Since the lead 92 has the ferrite chip 93 therein, however, if it is thinned, the wall of a portion thereof with the ferrite chip 93 therein also becomes thin. Since the lead and the like are made of resin in most cases, such thinning causes insufficient strength, and the lead 92 may undergo plastic deformation due to the load applied during operation. In a case in which the lead 92 is deformed inside the ferrite core 94, it may abut the inner wall of the ferrite core 94 and may be made unable to move. In this state, input operation with the input pen 90 is impossible. Consequently, it is difficult to thin the lead 92.
On the other hand, since the ferrite core 94 has a through hole in which the lead 92 extends, the through hole and the peripheral wall must be thinned in order to thin the ferrite core 94. In addition to the difficulty in thinning the lead 92, since ferrite is a fragile structural material, if the ferrite core 94 is excessively thinned, cracking may occur due to insufficient strength.
For example, in the step of winding the coil 95 on the ferrite core 94 in the production process of the input pen 90, tension of the wire is applied to the ferrite core 94. Furthermore, while such winding is performed in a state in which the ferrite core 94 is fixed, stress concentrates on the fixed portion of the ferrite core 94 due to the tension of the wire. Therefore, the ferrite core 94 must correspondingly have great strength. In consideration of vibrations during transportation and dropping shock tests for products, the strength which the ferrite core 94 should have is significantly great.
If the ferrite core 94 is cracked, the inductance of the coil 95 is lowered below its initial value, and the tuning frequency of the tuning circuit 99 is offset. For this reason, the input pen 90 may not work as the input device.
Therefore, the lead 92 and the ferrite core 94 in the input pen 90 must have a predetermined large strength, and it is difficult to reduce the size of the input pen 90 without changing the structure thereof.
Size reduction of electronic devices improves portability, but may decrease ease of input operation. For this reason, there has been a demand for a small input device that provides high operability.